Synergistic Rhizobium–PSB Consortium (NRA1–JCA-5) Optimizes Groundnut Productivity and Nutrient Use Efficiency (NUE) under Reduced Fertilization

Excessive synthetic fertilizer use undermines soil health, profitability, and sustainability in legume production. Here we validated a novel Rhizobium sp. NRA1 ( 99.2% identity to R. phaseoli ; GenBank PP355674)–PSB (Phosphate solubilizing bacteria) Priestia megaterium JCA-5 ( 99.6% identity to P. megaterium ; GenBank PP809390) consortium enabling 25% N-P fertilizer reduction in groundnut field trials while maintaining yields and enhancing nutrient efficiency. Two-year randomized block trials (loamy Inceptisol) demonstrated T₉ (Novel Rhizobium PSB consortium + 75% N-P + 100% K) achieved yield parity with 100% NPK (3679 kg ha⁻¹ vs. 3854 kg ha⁻¹ predicted), superior agronomic efficiency (AE: 23.76 kg yield kg⁻¹ nutrient), partial factor productivity (PFP: 36.79 kg kg⁻¹), and highest profitability (B:C 3.05). Enhanced nodulation (NEI > 640%), seed quality (oil 45.6%, protein 26.1%), and soil nutrient retention confirmed synergistic N₂ fixation and P solubilization. Multivariate analyses (heatmap–dendrogram) revealed mechanistic complementarity, with T₉ optimizing carbon partitioning and resource use. This field-validated consortium establishes a scalable model for fertilizer substitution, advancing climate-smart legume intensification.